[Field trial of an attenuated vaccine against heartwater disease]

The results are given of a field trial using a Senegalese stock of Cowdria ruminantium which had been attenuated by passage in cell culture. Thirty vaccinated and thirty control sheep were exposed in the Niayes region of Senegal and were monitored daily. In the control group, 22 animals died of heartwater, associated in one case with anaplasmosis. In the vaccinated group, 13 animals died; Cowdria was found only in two sheep which had previously suffered from ehrlichiosis or anaplasmosis; three other cases of ehrlichiosis and two of anaplasmosis were also observed among these 13 animals. The resistance of the two vaccinated animals which showed Cowdria in their cerebral cortex was apparently lowered by the intercurrent infections. The other animals of the vaccinated group showed no evidence of Cowdria infection.